Attention is a critical component of visual perception that allows the brain to allocate its limited resources depending on current task demands. Most research has focused on our ability to covertly attend to a specific region within the visual field (spatial attention), but we can also attend to a specific visual feature, independent of spatial position (feature-based attention). Studies of spatial attention have identified a network of higher-order areas in frontal and parietal cortex that appear to be the source of these modulating signals. Recent studies suggest that the frontoparietal network implicated in spatial attention may play a more general role in attentional processing. However, the role of this network in feature-based attention remains unclear due to methodological limitations of functional magnetic resonance imaging (fMRI) and the lack of single cell studies in the macaque. Using a combined behavioral, neuroimaging, and electrophysiological approach, this proposal will address the following specific aims to more clearly define the role of frontal and parietal regions in the control of feature-based attention. Aim 1: Identify regions of human frontal and parietal cortex that contribute to feature- and space-based attention using an fMRI-adaptation paradigm. Aim 2: Identify regions of the primate brain that have similar response properties compared to the human regions using virtually the same experimental design and methods. Aim 3: Characterize the neuronal response properties in regions involved in feature-based attention, particularly those that overlap with spatial attention, in primates using fMRI-guided single-unit recordings. These experiments will bridge the gap between indirect measure of neural activity in humans (fMRI) and single cell studies in monkeys and advance our understanding of the neural mechanisms and the network architecture contributing to top-down attentional control. The selection of relevant information from the natural environment is one of the most fundamental cognitive abilities for guiding behavior. Visual attention plays a prominent role in healthy brain functioning and is disrupted in a wide variety of brain disorders, such as ADHD, schizophrenia and spatial hemineglect following stroke. A more complete characterization of the mechanisms subserving normal attentional functions in the human brain will provide a platform from which to evaluate and alleviate these dysfunctions.